The present invention relates to a thin film magnetic head for detecting a magnetic signal recorded on a medium and, more particularly, to a thin film magnetic head having a mechanism for improving the precision of finish polishing of the medium-opposing surface and a manufacturing method of the same.
In general, as shown in FIG. 3, a thin film magnetic head 9 is formed with an electric lap monitor 10 as an end point detection means used when finish-polishing its medium-opposing surface 12. According to the general operation of the electric lap monitor 10, as shown in FIG. 4, during finish polishing of the medium-opposing surface 12, as polishing progresses, a pattern width h4 of a resistor 15 formed to be parallel to the medium-opposing surface 12 decreases gradually. Along with this decrease, the resistance detected between terminals 16a and 16b of the electric lap monitor 10 increases. When this resistance reaches a desired value, it is determined that the polishing end point has been reached.
When the resistance as the target of the polishing end point is fixed, variations in film thickness and resistivity of the resistor 15 cause variations in polishing end point. In a thin film magnetic head used in a magnetic disk device, even the most popular product requires a submicron-order precision in the polishing amount of its medium-opposing surface. For this reason, it is inappropriate to fix the resistance which is the target of the polishing end point.
In order to solve this problem, usually, a two terminal reference resistance 11 always showing a constant resistance is prepared separately from the electric lap monitor 10, as shown in FIG. 3, regardless of the progress of polishing or bar-like cutting as a pre-step in polishing.
FIG. 7 schematically shows the two terminal reference resistance 11. A resistor 27 of the two terminal reference resistance 11 is formed in accordance with the same process and material as those of the resistor 15 of the electric lap monitor 10 shown in FIG. 4. As shown in FIG. 3, if the distance between the resistor 27 and the resistor 15 is not very large, the resistivity and film thickness of the resistor 27 of the two terminal reference resistance 11 and those of the resistor 15 of the electric lap monitor 10 can be regarded as equal. Accordingly, the resistance of the resistor 27 of the two terminal reference resistance 11 is measured between terminals 28a and 28b, and the resistance as the target of the polishing end point can be calculated with reference to the measured resistance.
An example of the polishing method for the medium-opposing surface utilizing the electric lap monitor as described above is disclosed in, e.g., Japanese Patent Laid-Open No. 58-57613. More specifically, this reference describes a method of forming the electric lap monitor of a thin film magnetic head and that of a magnetoresistive effect type head in the same process of forming one of the constituent elements of the magnetic head, and the polishing amount of the medium-opposing surface is detected by using both the electric lap monitor and the reference resistance.
In the case of a thin film magnetic head, in a thin film magnetic head 30 shown in FIGS. 8A to 8B, the resistors of the electric lap monitor and the reference resistance are most generally formed in the same process of forming a magnetoresistive effect element film 31 made of a stacked film of an NiFe alloy or the like which is one of the constituent elements of a thin film magnetic head element 30a.
In the thin film magnetic head using the conventional two terminal reference resistance 11 shown in FIG. 7, when widths h3 and w3 of the resistor 27 of the two terminal reference resistance 11 vary, the resistance of the resistor 27 which is used for calculating the reference for the polishing end point of the medium-opposing surface 29 also varies.
In general, due to the limitation in the manufacture, it is difficult to suppress the variations in width of the resistor 27 within a range that does not influence the polishing precision, and the variations in width of the resistor 27 still directly appear as the variations in polishing end point.